electromagnetic separation
PTMS MAGNETIC SEPARATOR
what is magnetic separation in Quartz？
The research on high-purity quartz sand silica purification method is an extremely important class of optoelectronic materials, which are widely used in semiconductors and optical fibers through high-tech fields such as floodlight, laser and aerospace. As these areas become more stringent in terms of high purity silica impurity content, the demand for high purity silica is also increasing. At present, China needs to rely heavily on imported high-purity silica. Therefore, the use of quartz sand purification technology to obtain high-purity silica is an effective way to meet the needs of high-purity silicon high-tech fields, and is of great significance for promoting the development of China's national economy.
The main purpose of the quartz sand purification method can be divided into physical method and chemical method.
The physical methods of physical cleaning and classification methods are mainly desliming, scrubbing, magnetic separation, flotation and ultrasonic methods.
Washing off the mud and classifying 1.1 This method is mainly for quartz sand containing a lot of clay minerals. As the quartz sand particles are refined, the grade of SiO2 decreases, and the taste of impurities such as iron-aluminum minerals increases. Therefore, before the inclusion of quartz sand water ore, it is necessary to grade the mud, and the effect is more obvious. It is only a pretreatment method and is very common before the early application, but the removal effect due to the presence of quartz sand and iron mineral surface film is not significant.
1.2 Scrub scrub is the use of peeling force between force and mechanical scrub to remove impurities on the surface of sand film, clay and clay mineral quartz sand, further SAA unmatched monomer mineral aggregates, and then work to achieve the grade of quartz sand Further purification effect. Currently, there are two methods of bar and mechanical friction scrubbing. For mechanical scrubbing, the scrubbing and scrubbing effects of the mechanical equipment and processes associated with its structure and configuration are the main factors affecting the rubbing effect. Because there are many factors affecting it, the recovery rate of mechanical scrubbing is very low, only about 40%, so the effect of mechanical scrubbing is not ideal. Compared to mechanical scrubbing, friction bars work much better than washing. During the bar friction washing process,
1.3 Magnetic magnetic separation can remove silica particles containing some impurities, hematite, limonite and biotite are mainly impurities in weak magnetic minerals and ferromagnetic mineral magnetite. For minerals with weak magnetic impurities, a magnetic machine of 100,000 e or more is often used, which is weakened by a machine or a magnetic separator that frequently uses ferromagnetic mineral impurities. In general, the frequency and magnetic field strength of the iron removal effect of the iron remover have a significant effect. As the number of magnetic separations increases, the iron content decreases; and at a certain magnetic field strength, most of the iron can be removed, but even if the magnetic field The strength is much improved, and the iron removal ratio is not much changed. In addition, the quartz sand has a finer fineness, and the effect is better except for iron. The reason is that the fine quartz sand has a high iron content and impurities. Venus conducted an experimental study in the field of high-purity quartz sand purification process research. The results show that with the increase of magnetic field strength and impurity removal rate, the impurity removal rate is not obvious after the magnetic field strength reaches 100000e. Therefore a suitable magnetic field strength should be 100000e. After magnetic separation, 40 mesh SiO2 grade reaches 99.05%, Fe2O3 content is 0.071%: 40-80 mesh SiO2 grade 99.09%, Fe2O3 content 0.070%; 80-140 mesh SiO2 grade 99.14%, Fe2O3 content 0.067%: 140-200 mesh SiO2 Grade 99.10%, Fe2O3 content 0.069%. However, quartz sand containing impurities, especially when containing weaker magnetic or non-magnetic impurities, cannot be purified into high-purity quartz sand using only magnetic separation. 1.4 Flotation Quartz Sand Flotation In order to remove non-magnetic impurities associated with mineral feldspar and mica. There are currently flotation methods for fluorine and fluorine-free flotation. Flotation is the use of a fluorocationic collector and a hydrofluoric acid activator in the acidic pH range. However, considering the serious environmental impact of fluorine-containing waste, people began to turn to the use of fluorine-free floatation. Using quartz, the difference in feldspar structure constitutes a reasonable withered mixed ion trapping ratio and collector dosage, and two independent llo are realized by using different zeta potentials of the preferential floating feldspar. It has been reported that under neutral conditions, the addition of fluorine-free flotation reagent increases the SiO 2 content of the fine silica powder from 99.1% to about 99.77%, and the corresponding Fe 2 O 3 content decreases from 0.081% to 0.023%. The rate is between 83% and 85%. This indicates that fluorine-free flotation can significantly improve the quality of silica fine powder. Tang Yafei et al used sodium hexametaphosphate as dispersant and flotation modifier. Dodecylamine was used as a collector to remove iron impurities and reduce the Fe2O3 content from 0.09% to 0.02% from silica fine powder. The yield was 85%.
1.5 Ultrasonic ultrasonic method relies on acoustic wave propagation medium, which has mechanical energy, which will cause interaction with the medium during propagation and produce various effects (mechanical effect, thermal effect and cavitation effect). When the ultrasonic shredder head is used to act on the liquid, the inside of the liquid changes, generating pressure or tension. When the tension reaches a certain intensity, cavitation occurs, causing numerous small bubbles to be compressed with ultrasonic vibration, and the pressure is lowered; When the bubble reaches a critical size (the scale determines the frequency of the ultrasonic wave), these bubbles will burst, and the huge pressure in the liquid will have a severe impact on the solid particles, which will have a significant effect on the trace impurities or spray film on the surface of the particle. Under the action of the agent, it is quickly peeled off from the surface of the particles into fine suspended solids, which are separated from the quartz sand and washed, and the purity of the quartz sand is improved. A small amount of dispersant is added to the medium and medium such as Liaolan, and the quartz sand particles are deposited 0-15mm. After ultrasonic treatment, containing Fe2030.12%, S10299.42% quartz sand reaches Fe2030.01%, 8i0299.8%, recovery rate Up to 99%, reaching the standard optical glass sand.
2, quartz sand pickling chemical method
The chemical method is mainly acid leaching and complexation, and the acid leaching method utilizes the impurity characteristics of quartz which is insoluble in acid (except HF), minerals and the like which are soluble in acid, thereby further purifying quartz. After acid leaching, the quartz powder is used for complexation, which forms a coordination compound with the impurity ions in the solution, and further removes the impurity ions in the solution. The acid pickling acid leaching method is divided into a single acid method and a mixed acid leaching method.
Acid pickling acids are used, typically sulfuric acid, hydrochloric acid, nitric acid and hydrofluoric acid. The common oxalic acid and acetic acid are mainly quartz, and among these acids, there are good metal mineral impurities removed. It is obvious that the various acids for removing Pe and A1 are obvious, but the removal of Ti and Cr is mainly treated with concentrated sulfuric acid, aqua regia and hydrofluoric acid. The main factors affecting the acid treatment of acid concentration, temperature, time and washing process.
2.1 single acid leaching
A certain amount of acid solution is placed in a certain concentration of quartz sand, heated to a certain temperature, heated for a suitable time, the acid solution is recovered, the quartz sand is washed, and dried. A silty clay diatomite l'oJ from Sichuan is treated with sulfuric acid as the perfusate. By studying the temperature, sulfuric acid concentration and liquid-solid ratio, it is found that when the temperature is 90 ° C and the sulfuric acid concentration is 40%, the liquid-solid ratio is 10 :1, the leaching rate of diatomite iron is the best, the content of Fe20 is 3%-4% to 0.86%, the content of Al203 is reduced from 9.55% to 7.08%, and the content of SiO: diatomaceous earth is increased to over 80%. In the experimental study of quartz acid leaching purification, Roy Zhou studied the hydrofluoric acid leaching temperature, concentration, time,
2.2 mixed acid leaching
Since each acid removes impurities in different quartz sands, different acids are mixed together to produce a synergistic effect, so the removal rate of impurities in the quartz sand is higher, and quartz sand of higher purity can be achieved. After the quartz sand is rinsed with water, the acidic solution is added to the mixture, and the leaching time is generally stirred at ambient temperature for 24 hours. If heated, the mixture is leached for 2 to 6 hours, then washed and dried. Zhang Chang et al. used a liquid-solid ratio of 18% hydrochloric acid to silica fume at room temperature of 1.5:1, and then leached with 25% sulfuric acid, sulfuric acid and liquid-solid silica powder at a ratio of 2:1 for the second acid. The acid leaching time was 12h, and the iron content of the silica ash after the secondary acid leaching was < 60ug / g. The slurry containing the mechanical stirrer is placed in a capacitor to prepare a 20%-80% solid mass fraction of the eluted quartz sand, and then a hydrochloric acid solution (1% to 10%) and a hydrofluoric acid solution (1% quartz sand and a solution at 75) are added. Stir at -100 ° C for 2-3 h, then remove the slurry and wash several times with water until the wash shows a near neutral pH. After this method, the iron content of the quartz sand can be reduced from 0.0059% to 0.0002%. -0.005%. The proportion of succinic acid used is sulfuric acid: hydrochloric acid: nitric acid: 50% hydrofluoric acid: 25%: 15%: 10%, heated to 80 ° C, leaching pulp concentration is 50% - 55%, wherein oxidizing The content of ferrosilicon impurities reaches standard high purity quartz sand (SiO2 ≥ 99.98%, Fe2O3 ≤ 0.001%).
2.3 complexation
Complexation is a medium-strength organic acid that reacts with impurities on the surface of quartz sand and forms stable coordination compounds and impurity ions after the reaction, which reduces the concentration of impurity ions on the surface of the particles and prevents ions from being washed. In the middle, the impurity content of the silica sand is further reduced. Like the Panias 120, the average particle size is 110x10°20ltm quartz sand iron content, a certain amount is weighed and put into the oxalic acid solution, heated to 80 ° C, the treatment time is 3h, the iron-containing minerals are soluble in the acidic solution only It can form Fe3 +, Fe3 + and then form a stable chelate with oxalic acid, wherein the removal rate of iron is between 80% and 100%. After treatment, the iron content of quartz sand is less than 10x10-~. In Liuyang City, Hunan Province, the content of SiO2 in oxalic acid increased from 98.26% to 99.81%, the content of Al2O3 decreased from 0.18% to 0.15%, and the content of Fe2O3 decreased to 0.10%. The acid used above can be regenerated by evaporation, condensation or other means for reuse. When pure silica is required, the acidic wash water must be distilled water or deionized water, so the water contains iron and other impurities that contaminate the high purity silica.
2.4 Other methods
SiO2 has a wide range of applications, different applications, and different purity requirements. Therefore, other purification methods are sometimes used for further purification. For example, electrostatic separation is a small difference in electrical impurities between quartz and minerals. Select trace mineral impurities: dioxide. The silicon thermal burst method heats mineral inclusions to a certain temperature after the explosion, so that impurities in the inclusions are removed. The thermal chlorination method removes quartz minerals and impurities such as metal inclusions in the bubble phase.
